1. Field of the Invention
The present invention relates to a selectively called radio receiver, and a method for controlling this selectively called radio receiver, and more specifically, is directed to a technique for monitoring error operations of a control unit employed in the selectively called radio receiver.
2. Description of the Related Art
In general, conventional selectively called radio receivers have rescue means used when control units are erroneously operated due to some reason, and thereafter the control units cannot be recovered to the normal operations. However, operations in such a case that the normal operation is again commenced after this erroneous (error) operation are not guaranteed.
When the conventional selectively called radio receiver is recovered from the error operation condition to the normal operation condition, the control unit thereof cannot recognize that this control unit was erroneously operated in the past. As a consequence, for example, even when the information stored in the memory is electrically destroyed by the error operation, the succeeding process operation can be continued in this control unit. As a result, there is a risk that the secondary error operation is conducted due to the execution of this succeeding process operation.
Also, the access operation to such a memory region other than the memory region to which the control unit is allowed to access may give adverse influences to the lifetime of the cell. In other words, there is such a risk that the access operation to such a memory region other than the memory region to which the control unit is allowed to access is carried out in combination with the data having the floating (intermediate) potential other than either the logic level "1" or the logic level "0". Also, there is another risk that when the write protection region is write-accessed, the potential of the logic level "1" may collide with the potential of the logic level "0" on the same signal line. In this potential collision case, the impedance between the power supply and the ground becomes low, so that the penetration current may flow. As a result, the power consumption is increased to thereby shorten the lifetime of the cell.
As one conventional technical solution, for instance, the Japanese Laid-open Patent Disclosure JP-A-Heisei 2-141837 opened in 1990 discloses "Microprocessor Controlling System". This microprocessor controlling system is directed to detect the runaway phenomenon of this microprocessor and to perform the abnormal condition rescue process.
To achieve this purpose, this conventional microprocessor control system employs such a memory that the redundant memory regions are additionally provided with the respective memory regions. Into this redundant memory region, the discrimination information is written by which the normally-program-stored memory region can be discriminated from the program-not-stored memory region. Then, when the microprocessor accesses to the memory region, the content of the redundant memory region added to the accessed memory region is referred, the microprocessor can discriminate whether this access operation belongs to normal access operation, or the abnormal access operation. As a result of this discrimination, when the abnormal access operation is carried out, the microprocessor performs the abnormal access rescue process. Accordingly, in such a case that while the microprocessor executes the program, when the memory region other than the memory region into which the program is normally stored is referred, the microprocessor judges that the abnormal condition happens to occur, and therefore performs the abnormal access rescue process.
However, in this conventional microprocessor control system, the redundant memory regions should be additionally provided with all of the address spaces to which the microprocessor will possibly access. As a consequence, there is a problem that the memory having the large capacity is required.